Design Of Coded Aperture Collimator And Digital Image Reconstruction In Gamma-ray Camera

Gamma-ray camera is a equipment for gamma-rays imaging. It's widely applied in the fields, such as nuclear detecting, nuclear medicine, nuclear radiation, environmental monitoring and national security and so on. The current gamma cameras are being developed for the better properties with high sensitivity, high resolution, high signal-to-noise ratio(SNR)and convenience for handing etc. Recently, coded aperture collimator with its unique characteristics, as a potential candidate for replacing the pinholes and parallel holes collimator and satisfying the trends of gamma-ray camera, is studied extensively. There are still a lot of problems remained.In this thesis, the design of coded aperture collimator and digital imaging reconstruction in the gamma-ray camera are studied. At the first , the principles of coded aperture imaging are introduced, and the characteristics of different kinds of coded apertures are analyzed. A mosaic modified uniformly redundant arrays(MURA)(11×11)mask with high sensitivity and resolution for the gamma camera is designed and optimized, the results are performed and discussed. And then, A general procedures of coded aperture collimator design is summarized and proposed.On the other hand, based on Poisson statistic model, the Maximum-Likelihood and Expectation-Maximization (MLEM) iterative reconstruction algorithm in the coded aperture imaging for 2D and 3D objects are derived respectively. By analyzing the characteristics of 2D tomography MLEM algorithm, a method of estimating the appropriate iterative frequency is brought out. The quality of reconstruction imaging with two kinds of algorithms is compared by computer simulation .The mosaic MURA mask has been applied to a gamma-rays imaging system and the results of preliminary experiments show that field-of-view (FOV) and resolution are in accordance with those of theory predicted. In addition, point sources image could be recovered by the MLEM and correlation decoded algorithms and the quality of reconstruction image by MLEM algorithm is better than that by decode algorithm. It's agreeable with the results of computer simulation. So it's verified that the scheme of coded aperture imaging technique is feasible and the MLEM reconstruction algorithm is rational. Finally a correcting method in the case of high energy isotopes imaging is presented and identified by experiments.